Hitherto, a decorative coating method has been often employed as a method for increasing the variety of decorations on resin molding made of a thermoplastic resin. Generally, according to a conventional coating methods, molding formed through injection molding in a mold is removed from the mold and then the molding is applied a coating material onto a surface of the molding by means of a spraying method, an immersion method, or the like. The coating material applied onto the surface of the molding is subsequently dried and thus turned into a hard coating material film (coating film) to coat the surface of the molding and decorate and protect the surface of the molding.
In recent years, however, proposed is an in-mold coating formation method (also called an in-mold coating method) which performs resin molding and application of a coating material in the same mold for the purpose of reducing the number of steps in the coating method. According to the in-mold coating formation method, after injection molding of a rein in a mold, the mold is slightly opened to form a space between resin molding formed in the mold and a mold cavity surface. Then, a coating material is injected into the space using a coating material injecting unit, after which the mold is clamped again to thereby uniformly spread the coating material over the molding surface. After that, the coating material is hardened and the molding is coated.
According to the in-mold coating formation method, since a thermoplastic resin is molded and coated in the same mold, a cost can be saved because of a simplified process and in addition, any failure rarely occurs due to adhesion of dust in the air to a pre-hardened coating material, and a high-quality product can be provided. Thus, there has been considered the application of the in-mold coating formation method to especially production of many components for use in automobiles such as a bumper, a door mirror cover, and a fender, which require a high-quality appearance.
Many in-mold coating formation methods use a mold having an engagement portion (hereinafter also referred to as a “landed portion”) of a landed structure (shore edge structure) formed around the entire circumference of a mold cavity to prevent leakage of a coating material. In practice, however, there is a problem that the leakage of a coating material from the mold cavity cannot be completely prevented by the landed portion alone.
To overcome such a problem, a mold for in-mold coating formation has been proposed. The mold has an auxiliary cavity around the entire circumference of a mold cavity and the auxiliary cavity is filled with a resin to prevent leakage of a coating material (for example, see Patent Document 1). This mold for in-mold coating formation has an advantage that the coating material rarely leaks even if the landed portion is worn out.
[Patent Document 1]
JP 2001-138334 A
[Patent Document 2]
JP 3843833 B